It is known that macrophage cells have phagocytosis, and this macrophage phagocytosis allows innate immunity such as ingestion, degradation and elimination of foreign substances such as pathogenic bacteria, and allows acquired immunity through the process of presentation of antigen information on the surface of macrophage cells, its transmission to T-lymphocytes, induction of specific antibody production and so forth. In addition, it is known that macrophages produce various cytokines, and the produced cytokines exhibit various actions such as regulating inflammatory responses and immune responses, inducing apoptosis, or acting as a hematopoietic factor or growth factor. Therefore, activation of the phagocytosis of macrophages or cytokine production in macrophages leads to enhancement of animal immunity, and substances effective for the activation are useful as an active ingredient of a new immunostimulator, immunomodulator, anticancer agent, anti-allergic agent, adjuvant for antibody production, or the like. They are particularly useful as an immunostimulator, immunomodulator, anticancer agent, or anti-allergic agent in which innate immunity or cellular immunity is involved.
Regarding substances effective for the activation of macrophage phagocytosis, the enhancement of phagocytic activity of macrophages by PLGA (poly(lactic acid/glycolic acid) copolymer), including PLGA with a molecular weight of 1,500 to 150,000, is described, for example, in the following Patent Literature 1 or 2. In addition, regarding substances for promoting cytokine production, the promotion of cytokine production by alginate oligomer prepared from sodium alginate is described, for example, in the following Patent Literature 3.